Hydrophilic fluoroplastic substrates

ABSTRACT

Hydrophilic fluoroplastic substrates and methods of making hydrophilic fluoroplastic substrates from 4-acryloylmorpholine are disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/787,573, filed Oct. 28, 2015, which is a national stage filingunder 35 U.S.C. 371 of PCT/US2014/040784, filed Jun. 4, 2014, whichclaims priority to U.S. Provisional Application No. 61/836,467, filedJun. 18, 2013, the disclosure of which is incorporated by reference inits/their entirety herein.

TECHNICAL FIELD

The present disclosure relates to hydrophilic fluoroplastic substrates,and methods for preparing the same. In one embodiment such hydrophilicfluoroplastic substrates may be used as filtration media.

SUMMARY

There is a need in the art for fluoroplastic substrates having enhancedhydrophilicity. Further, there is a need in the art for a method ofmaking fluoroplastic substrates having enhanced hydrophilicity. Further,there is a need in the art for a method of making porous fluoroplasticsubstrates having enhanced hydrophilicity while maintaining orincreasing the flux of liquids through the substrate.

The present disclosure is directed to hydrophilic substrates and methodsof making hydrophilic substrates. More specifically, the hydrophilicsubstrates include a fluoroplastic substrate that has beensurface-treated to provide the requisite hydrophilicity.

In one aspect, a method of treating a fluoroplastic substrate isdescribed comprising:

-   -   (a) providing a fluoroplastic substrate comprising a polymer        having a structural unit selected from —CHF—, —CH₂CF₂—, or        —CF₂CH₂—;    -   (b) contacting the fluoroplastic substrate with a composition        comprising 4-acryloylmorpholine; and    -   (c) exposing the fluoroplastic substrate to a controlled amount        of ionizing radiation selected from at least one of e-beam,        x-ray, and gamma radiation so as to form a surface treatment on        the fluoroplastic substrate comprising a grafted,        radiation-initiated reaction product of the composition        comprising 4-acryloylmorpholine attached to the surfaces of the        fluoroplastic substrate

In another aspect, an article is described comprising: a porousfluoroplastic substrate comprising a polymer having a structural unitselected from —CHF—, —CH2CF2-, or —CF2CH2- and having interstitial andouter surfaces; and a surface-treatment thereon the porous fluoroplasticsubstrate, wherein the surface-treatment is a grafted reaction productof a composition comprising 4-acryloylmorpholine.

In yet another aspect, an article is described comprising: afluoroplastic substrate comprising a polymer having a structural unitselected from —CHF—, —CH₂CF₂—, or —CF₂CH₂—; and a surface-treatmentthereon the fluoroplastic substrate, wherein the surface-treatment is agrafted reaction product of a composition comprising4-acryloylmorpholine and a second monomer.

In yet another aspect, a method of filtering a liquid is describedcomprising the surface-treated fluoroplastic substrate described herein.

In yet another aspect, a graft copolymer composition is describedcomprising a fluoropolymer that is grafted to at least one of: monomer,oligomer, and polymer formed from a monomer comprising4-acryloylmorpholine; wherein the fluoropolymer is formed from monomerscomprising (i) ethylene and chlorotrifluoroethylene, (ii) ethylene andtetrafluoroethylene, or (iii) tetrafluoroethylene, hexafluoropropylene,and vinylidene fluoride.

These and other features and advantages of the present invention willbecome apparent after a review of the following detailed description ofthe disclosed embodiments and the appended claims.

DETAILED DESCRIPTION

As used herein, the term

“a”, “an”, and “the” are used interchangeably and mean one or more;

“and/or” is used to indicate one or both stated cases may occur, forexample A and/or B includes, (A and B) and (A or B);

“copolymer” means a polymer comprising repeating units derived from atleast two different monomers and includes copolymers, terpolymers, etc.;and

“homopolymer” means a polymer comprising repeating units derived fromone monomer.

Also herein, recitation of ranges by endpoints includes all numberssubsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75,9.98, etc.).

Also herein, recitation of “at least one” includes all numbers of oneand greater (e.g., at least 2, at least 4, at least 6, at least 8, atleast 10, at least 25, at least 50, at least 100, etc.).

Fluoroplastics are an attractive choice for applications requiringtemperature, chemical, and/or environmental resistance. However, the lowsurface energies of these materials can be detrimental in someapplications. Therefore, the present disclosure is directed towardproviding a surface treatment to the fluoroplastic substrate to improveits hydrophilicity.

Monomers may be grafted onto polymer base substrates to improve theproperties of the base substrate. For example U.S. Pat. No. 6,828,386(MacKinnon) discloses exposing a polymeric base material to a dose ofionizing radiation, and then contacting the irradiated base materialwith a microemulsion comprising a fluorostyrenic monomer to prepare ionexchange membranes, while U.S. Pat. Publ. Nos. 2010/0209693 and2010/0210160 (Hester et al.) disclose a base substrate and a gammaradiation-initiated product of a monomer comprising a (meth)acrylatedgroup and at least one additionally free-radically polymerizable groupto prepare hydrophilic porous articles.

In the present disclosure, articles and methods are described whereinhydrophilic articles are provided by a process of ionizing (i.e., gamma,x-ray, and/ore-beam) radiation-initiated grafting of a free-radicallypolymerizable monomer, 4-acryloylmorpholine (also known asN-acryloylmorpholine) onto a fluoroplastic substrate. The hydrophilicarticle of the present disclosure comprises a number of componentsincluding, but not limited to, (1) a fluoroplastic substrate and (2) anionizing radiation-initiated reaction product of a compositioncomprising 4-acryloylmorpholine.

Fluoroplastic Substrate

The base substrate is a fluoroplastic (i.e., a plastic that includesfluorine atoms). In the present disclosure, the fluoroplastic substratecomprises a polymer with a repeating structural unit selected from atleast one of: —CHF—, —CH₂CF₂—, or —CF₂CH₂—, wherein repeating in thiscontext means the structural unit is present multiple times in or alongthe polymer chain. In other words, the fluoroplastic substrate comprisesat least 5, 10, 20, or even 100 structural units selected from at leastone of: —CHF—, —CH₂CF₂—, or —CF₂CH₂— in the polymer chain. In oneembodiment, at least 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 95, 98,or 99 wt. % of the polymer will comprise structural units selected fromat least one of: —CHF—, —CH₂CF₂—, or —CF₂CH₂—. Such structural units arederived from the polymerization of various monomers. For example: thepolymerization of vinyl fluoride; the polymerization of vinylidenefluoride; the copolymerization of a hydrocarbon olefin (such as ethyleneand/or propylene) and fluorinated monomers (such aschlorotrifluoroethylene, tetrafluoroethylene, and/orhexafluoropropylene). Homopolymers and copolymers of vinylidenefluoride; homopolymers and copolymers of vinyl fluoride; copolymers ofhydrocarbon olefins (such as ethylene and/or propylene) and fluorinatedmonomers (such as chlorotrifluoroethylene, hexafluoropropylene,tetrafluoroethylene, perfluorinated allyl ethers, and/or perfluorinatedvinyl ethers); and homopolymers and copolymers comprising fluorinatedmonomers all possess such structural units. Alternatively, thefluoroplastic substrate comprises at least 5, 10, 20, or even 100structural units selected from at least one of: —CHF—, —CH₂CFX—, or—CFXCH₂— in the polymer chain, wherein X is Cl or F. In one embodiment,at least 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 95, 98, or 99 wt. %of the polymer will comprise structural units selected from at least oneof: —CHF—, —CH₂CFX—, or —CFXCH₂-, wherein X is Cl or F. Exemplaryfluoroplastic substrates include, ECTFE (a copolymer of ethylene andchlorotrifluoroethylene), ETFE (a copolymer of ethylene andtetrafluoroethylene), THV (a terpolymer oftetrafluoroethylene/hexafluoropropylene/vinylidene fluoride), VDF-CTFE(a copolymer of vinylidene fluoride and chlorotrifluoroethylene), andpolyvinylidene fluoride (PVDF). In one embodiment of the presentdisclosure, the fluoroplastic substrate is not polyvinylidene fluoride(PVDF).

The fluoropolymers of the fluoroplastic substrate can be synthesized byvarious methods including solution, dispersion, and most commonly,emulsion polymerization as known in the art. Typically, thepolymerization is a free radical, addition polymerization reaction. Thecopolymerization of ethylene with chlorotrifluoroethylene ortetrafluoroethylene is known to occur by predominantly an alternatingmechanism wherein the addition of an ethylene monomer andchlorotrifluoroethylene or tetrafluoroethylene alternates. In additionto the fluoropolymers, the fluoroplastic substrate can containinitiators and their fragments, processing aids, antioxidants, andsurfactants, such as the alkali metal salts of perfluorooctanoic acid orother fluorinated surfactants as described in U.S. Pat. No. 4,482,685(Chandrasekaran et al.), U.S. Pat. No. 7,989,566 (Coughlin et al.), U.S.Pat. No. 7,999,049 (Coughlin et al.), and U.S. Pat. No. 7,671,112(Dadalas et al.).

The fluoroplastic substrate is not particularly limited in thickness,but it depends on the application. For example, if the treatedfluoroplastic substrate is to be used as a filtration membrane, thethickness of the fluoroplastic substrate should be kept reasonably thinto limit the amount of pressure drop during the filtration. In oneembodiment, the fluoroplastic substrate has a thickness of at leastabout 10 micrometers (μm), 25 μm, 50 μm or even 75 μm; and no more than250 μm, 400 μm, 500 μm, 750 μm, 1000 μm, 1.5 millimeters (mm), 5 mm, oreven 1 centimeter.

The fluoroplastic substrate may be in any form such as a film, a fiber,a hollow fiber, a tube, a particle, a pellet, or a sheet. Thefluoroplastic substrate may be incorporated into various configurations,such as rolls, cylinders, cones, flat discs, pleated sheets, or spiralwound.

In one embodiment, the fluoroplastic substrate is dense or nonporous.

In another embodiment, the fluoroplastic substrate is porous, meaningthat the fluoroplastic substrate comprises a series of interconnectedpores from a first major surface of the fluoroplastic substrate to anopposing second major surface of the fluoroplastic substrate. The porousfluoroplastic substrate comprises outer surfaces as well as interstitialsurfaces which can comprise the gamma, x-ray, and/or e-beamradiation-initiated reaction product of the composition comprising4-acryloylmorpholine. Such porous fluoroplastic substrates includeporous films and nonwovens. In one exemplary embodiment, the porousfluoroplastic substrate has an average pore size that is greater thanabout 5 nanometers (nm), 10 nm, 20 nm, 50 nm, or even 100 nm; and lessthan about 30 μm, 25 μm, 20 μm, 15 μm, 10 μm, 5 μm, 2 μm, 1.5 μm, 1 μm,800 nm, 700 nm, 500 nm or even 300 nm.

In some embodiments, the substrate is a porous membrane such as athermally-induced phase separation (TIPS) membrane. TIPS membranes areoften prepared by forming a homogenous solution of a thermoplasticmaterial and a diluent, and optionally including a nucleating agent, bymixing at elevated temperatures in plastic compounding equipment, e.g.,an extruder. The solution can be shaped by passing through an orificeplate or extrusion die, and upon cooling, the thermoplastic materialcrystallizes and phase separates from the diluent. The crystallizedthermoplastic material is often stretched. The diluent is optionallyremoved either before or after stretching, leaving a porous polymericstructure. Porous membranes are further disclosed in U.S. Pat. No.4,539,256 (Shipman), U.S. Pat. No. 4,726,989 (Mrozinski), U.S. Pat. No.4,867,881 (Kinzer), U.S. Pat. No. 5,120,594 (Mrozinski), U.S. Pat. No.5,260,360 (Mrozinski et al.), U.S. Pat. No. 5,962,544 (Waller), and U.S.Pat. No. 6,096,293 (Mrozinski et al.) all of which are assigned to 3MCompany (St. Paul, Minn.), and each incorporated herein by reference.Useful ECTFE membranes may be prepared according to U.S. Pat. No.4,623,670 (Miura et al.); U.S. Pat. No. 4,702,836 (Miura et al.); U.S.Pat. No. 6,559,192 (Maccone et al.); and U.S. Pat. No. 7,247,238 (Mulleret al.); and U.S. Publ. No. 2011/0244013 (Mrozinski et al.).

Some exemplary TIPS membranes comprise poly(vinylidene fluoride) (PVDF),and copolymers of ethylene/chlorotrifluoroethylene (ECTFE). For someapplications, a TIPS membrane comprising ECTFE is particularlydesirable. TIPS membranes comprising ECTFE are further described in U.S.Publ. No. 2011/0244013 (Mrozinski et al.), incorporated herein byreference. For some applications, a TIPS membrane comprising PVDF isparticularly desirable. TIPS membranes comprising PVDF are furtherdescribed in U.S. Pat. No. 7,338,692, (Smith et al.), incorporatedherein by reference.

In some embodiments, the substrate is a porous membrane such as asolvent-induced phase separation (SIPS) membrane. SIPS membranes areoften made by preparing a homogeneous solution of a polymer in firstsolvent(s), casting the solution into desired shape, e.g. flat sheet orhollow fiber, contacting the cast solution with another second solventthat is a non-solvent for the polymer, but a solvent for the firstsolvent (i.e., the first solvent is miscible with the second solvent,but the polymer is not). Phase separation is induced by diffusion of thesecond solvent into the cast polymer solution and diffusion of the firstsolvent out of the polymer solution and into the second solvent, thusprecipitating the polymer. The polymer-lean phase is removed and thepolymer is dried to yield the porous structure. SIPS is also calledPhase Inversion, or Diffusion-induced Phase Separation, orNonsolvent-induced Phase Separation, such techniques are commonly knownin the art. Porous PVDF substrates can be made via a SIPS process, asPVDF dissolves in common organic solvents.

In one embodiment, a combination of a TIPS process and a SIPS process isused to prepare a porous substrate. See for example, U.S. Pat. No.7,632,439 (Mullette et al.), which discloses a process for making ECTFE,which is incorporated herein by reference.

Useful porous substrates include symmetric, asymmetric, or multizonemembranes, as well as multiple layers of such membranes. A symmetricmembrane is one having substantially the same average pore size and/orporosity throughout its thickness. An asymmetric membrane is a membranehaving a linear or non-linear gradient in average pore size and/orporosity extending from one major surface to an opposing major surfaceof the fluoroplastic substrate. In other words, the ratio of the averagepore size of the one major surface with the larger pores to the averagepore size of the opposing surface is greater than 3 or even greater than4. A multizone membrane is a membrane having two or more substantiallydistinct through-thickness zones, or layers having different averagepore sizes and/or different porosities. Multizone membranes are oftendesignated by the number of layers or zones, (e.g. a 2-zone membrane hastwo substantially distinct zones having different average pore sizes ordifferent porosities).

In other embodiments, the fluoroplastic substrate is a nonwoven web,which may include nonwoven webs manufactured by any of the commonlyknown processes for producing nonwoven webs. As used herein, the term“nonwoven web” refers to a fabric that has a structure of individualfibers or filaments which are randomly and/or unidirectionally interlaidin a mat-like fashion. For example, the fibrous nonwoven web can be madeby carded, air laid, spunlaced, spunbonding or melt-blowing techniquesor combinations thereof. Spunbonded fibers are typically formed byextruding molten thermoplastic polymer as filaments from a plurality offine, usually circular capillaries of a spinneret with the diameter ofthe extruded fibers being rapidly reduced. Meltblown fibers aretypically formed by extruding the molten thermoplastic material througha plurality of fine, usually circular, die capillaries as molten threadsor filaments into a high velocity, usually heated gas (e.g. air) stream,which attenuates the filaments of molten thermoplastic material toreduce their diameter. Thereafter, the meltblown fibers are carried bythe high velocity gas stream and are deposited on a collecting surfaceto form a web of randomly disbursed meltblown fibers. Any of thenon-woven webs may be made from a single type of fiber or two or morefibers that differ in the type of thermoplastic polymer, thicknessthereof, or both.

Useful porous fluoroplastic substrates of the present disclosure includethose made from PVDF, ETFE, ECTFE, and VDF-CTFE.

Composition

The composition of the present disclosure comprises the grafting monomer4-acryloylmorpholine, also referred to as N-acryloylmorpholine.

In one embodiment, the composition further comprises at least one secondmonomer selected from free radically polymerizable, ethylenicallyunsaturated compounds, such as acrylates, methacrylates, acrylic acids,methacrylic acids, acrylamides, methacrylamides, N-vinyl amides, vinylesters, styrenes, dienes, and combinations thereof.

In some embodiments, the 4-acryloylmorpholine can improve theperformance of the surface treatment (e.g., increase the criticalsurface tension of a surface-treated substrate, increase the CWST of asurface-treated porous substrates as defined in the test methods of theExamples section, decrease the amount of time to pass a given volume ofliquid through a surface-treated porous substrate, i.e., increase theflux, and/or decrease the static contact angle of a drop of water on asurface-treated substrate) of the second monomer.

In another embodiment, the second monomer can interact synergisticallywith the 4-acryloylmorpholine, achieving improved performance comparedto the individual monomer alone. Such an exemplary monomer includesdiacetone acrylamide, also known asN-(1,1-dimethyl-3-oxobutyl)acrylamide. In one embodiment of the presentdisclosure, the composition comprises 4-acryloylmorpholine and diacetoneacrylamide, wherein the weight percent of the diacetone acrylamide basedon the total weight of the 4-acryloylmorpholine and diacetone acrylamideis greater than 0, 1, 5, 10, or even 20%; and no more than 70, 60, 55,50, 45, or even 40%.

In one embodiment, the composition comprises at least one additive, suchas a chain transfer agent, an anti-oxidant, a surfactant, andcombinations thereof. Chain transfer agents control the molecular weightof the resultant polymer. They act to terminate the polymerizationprocess for a forming polymer, causing the polymer to have a shorterchain length, and thus a lower molecular weight, than it might otherwisehave. In general, the more chain transfer agent added, the lower themolecular weights of the resulting polymers. Examples of useful chaintransfer agents include, but are not limited to, those selected from thegroup consisting of chlorine, bromine, and iodine containing compounds,isopropyl alcohol, mercaptans, amines, and mixtures thereof. Thepreferred chain transfer agents are isopropanol, mercaptans such asisooctylthioglycolate and carbon tetrabromide. In one embodiment, thecomposition may comprise up to 0.5 parts by weight of a chain transferagent, typically about 0.02 to about 0.15 parts by weight, preferablyabout 0.02 to about 0.1 parts by weight, most preferably 0.03 to about0.07 parts by weight, based upon 100 parts by weight of the total of thecomposition. In one embodiment, the composition may comprise about 0.005to 5 parts of an anti-oxidant based upon 100 parts by weight of thetotal of the composition. In one embodiment, the composition maycomprise about 0.005 to 5 parts of a surfactant based upon 100 parts byweight of the total of the composition.

In one embodiment, the 4-acryloylmorpholine, and optional secondmonomer, and optional additive may be dissolved and/or suspended in oneor more solvents wherein a solvent is selected from an organic solventand/or water. The solvents should be chosen so that the monomersdissolve or disperse. Examples of useful solvents include, but are notlimited to, those selected from the group consisting of ketones,alcohols, ethers, esters, amides, hydrocarbons, halogenatedhydrocarbons, halocarbons, water, and mixtures thereof. Preferredsolvents are those that undergo relatively little chain transfer withradical species, such as the solvents of methanol and water, and theirmixtures. In one embodiment, the composition may comprise about at least40, 50, 60, 70, 75, 80, and at most 90, 95, and 99 wt. % of a solventbased on the total weight of the composition. Solvents (and anyungrafted materials) can be removed from the treated substrate byextraction or rinsing with solvent or drying or both. Drying can beaccomplished at ambient conditions or at elevated temperatures andpressures below or above atmospheric pressure. Impingement of gases suchas air or nitrogen can be used to dry.

As used herein “composition” and “composition comprising4-acryloylmorpholine” are used interchangeably to mean inclusion of the4-acryloylmorpholine along with any additional components includingsecond monomers, additives, and solvents, unless otherwise specified. Inone embodiment, the total concentration of the monomers in thecomposition ranges from about at least 1, 5 or even 10 wt. %; and atmost 20, 25, 30, 40, 50, or even 60 wt. % based on a total weight of thecomposition.

In the present disclosure, a monomer (e.g., 4-acryloylmorpholine) hasbeen found to unexpectedly achieve improved hydrophility of afluoroplastic substrate as compared to monomers that are more polarand/or have larger solubility parameters (e.g., Hansen solubilityparameter). For example, solubility parameters are related to cohesiveenergy density, and generally, the greater the solubility parameter, thegreater the cohesive energy density, and the greater the surfacetension. Thus, one would expect surfaces grafted with monomer having ahigher solubility parameter to have, for example, higher criticalsurface tension.

In general, fluorocarbons have much lower dispersive forces thanhydrocarbons and the two are not compatible. However, the fluoroplasticsubstrates of the present disclosure have both fluorocarbon andhydrocarbon content. Without wishing to be bound by theory it isbelieved that the fluorocarbon and hydrocarbon content increases thedispersive forces relative to perfluorinated materials and also providesdipoles and hydrogen bonding sites for potential interaction. As can beseen in the Example Section below, 4-acryloylmorpholine appears topossess the proper balance of dispersive, polar, and hydrogen bondingelements to both foster adsorption to and possibly plasticization of thefluoroplastic surface and, once grafted, provides a hydrophilic surface.

In the present disclosure, the resultant hydrophilic articles comprise afluoroplastic substrate and an ionizing radiation-initiated reactionproduct of the composition comprising 4-acryloylmorpholine. Thisionizing radiation-initiated reaction product of the compositioncomprising 4-acryloylmorpholine can be thought of as a second layergrafted on top of the fluoroplastic substrate. This second layer isconforming to the surface of the fluoroplastic substrate and it may becontinuous or discontinuous across the surface of the fluoroplasticsubstrate.

In one embodiment, when the fluoroplastic substrate is nonporous, thesurface treatment (or second layer) is continuous across the surface ofthe fluoroplastic substrate (in other words, at least 85, 90, 95, 99, oreven 100% of the surface, which was contacted with the compositioncomprises a gamma, x-ray, and/or e-beam radiation-initiated reactionproduct of the composition).

When discussing porous fluoroplastic substrates, a substantial portionof the surfaces (including the outer and intersistial surfaces) of theporous fluoroplastic substrates may comprise the surface treatment (orsecond layer) for example at least 65, 70, 75, 80, 85, 90, 95, 99, oreven 100% of the surfaces comprise an ionizing radiation-initiatedreaction product of the composition.

In one embodiment, the surface-treated fluoroplastic substrate comprisesan additional layer. This additional layer is in direct contact with thesurface-treated fluoroplastic substrate. In one embodiment, theadditional layer is provided on the side of the fluoroplastic substrateopposite the surface treatment. In another embodiment, the additionallayer is provided on the same side as the surface treatment. Theadditional layer may be a coating applied to the surface-treatedsubstrate that is adhered to surface-treated substrate. Such additionallayers may be used, for example, to provide mechanical support to thesurface-treated fluoroplastic substrate, temporarily protect a surfaceof the surface-treated fluoroplastic substrate (e.g., betweenmanufacture and point of use), and/or to provide additional performancefeatures to the surface-treated fluoroplastic substrate. For example, inone embodiment, when the articles are porous, the surface-treated,porous fluoroplastic substrate comprises an additional porous layer suchas a non-woven. The pores of the additional layer are larger than thepores of the fluoroplastic substrate. This article could be used in afiltration system, wherein the liquid to be filtered is first passedthrough the additional porous layer and then passed through thesurface-treated fluoroplastic substrate or alternatively, wherein theliquid to be filtered is first passed through the surface-treatedfluoroplastic substrate and then passed through the additional porouslayer.

Because the grafting of the composition onto the fluoroplastic substrateresults in a more hydrophilic surface that improves the fluoroplasticsubstrate's wettability by aqueous and hydrocarbon liquids, in oneembodiment of the present disclosure, the outer surface (or majorsurface) of the surface-treated fluoroplastic substrate comprising thereaction product of the composition comprising 4-acryloylmorpholine issubstantially free of an additional layer, for example a metal foil, orother non-porous layer that would preclude wetting of thesurface-treated fluoroplastic surface with liquids. In other words, thecomposition comprising the 4-acryloylmorpholine is used to make thesurface of the fluoroplastic substrate hydrophilic and not act as anadhesion promoter between the fluoroplastic substrate and an additionallayer.

Method of Making

The resultant hydrophilic substrates of the present disclosure may beprepared using a combination of process steps.

In one embodiment, the method comprises:

1) providing a fluoroplastic substrate,

2) contacting the fluoroplastic substrate with a composition comprising4-acryloylmorpholine,

3) exposing the fluoroplastic substrate comprising the composition to acontrolled amount of ionizing radiation so as to form a surfacetreatment on the fluoroplastic substrate comprising a grafted,radiation-initiated reaction product of the composition comprising4-acryloylmorpholine attached to the surfaces of the fluoroplasticsubstrate.

In this method, the fluoroplastic substrate is contacted with thecomposition prior to the irradiation step. As long as the compositiondoes not evaporate, the substrate comprising the composition may be heldfor more than an hour or even days before exposure to the radiation. Ifa continuous process is employed, the irradiation step may moretypically occur within minutes or even seconds after contacting thefluoroplastic substrate with the composition.

In another embodiment, the method comprises:

1) providing a fluoroplastic substrate,

2) exposing the fluoroplastic substrate to a controlled amount ofionizing radiation, and

3) contacting the fluoroplastic substrate with a composition comprising4-acryloylmorpholine so as to form a surface treatment on thefluoroplastic substrate comprising a grafted, radiation-initiatedreaction product of the composition comprising 4-acryloylmorpholineattached to the surfaces of the fluoroplastic substrate.

In this method, the fluoroplastic substrate is first exposed to theionizing radiation and then contacted with the composition comprisingthe 4-acryloylmorpholine. Typically the irradiated fluoroplasticsubstrate is contacted with the composition within an hour, preferablywithin minutes or even within seconds after being irradiated.

In the contacting steps mentioned above, the fluoroplastic substrate iscontacted with the composition comprising the 4-acryloylmorpholine.Suitable methods of contact include, but are not limited to, spraycoating, flood coating, knife coating, Meyer bar coating, dip coating,and gravure coating. When using porous fluoroplastic substrates, often,the porous fluoroplastic substrate is saturated with the composition, toenable the grafting monomers time to diffuse into the porous network ofthe substrate, enabling a surface-treatment of the interstitial surfacesthroughout the thickness of the fluoroplastic substrate. However, in oneembodiment, only a portion of the thickness of the porous fluoroplasticsubstrate comprises surface-treatment of the interstitial surfaces, dueto, for example, insufficient saturating time, difficulty in diffusingthe composition through the interconnected pore network, or the desireto only surface-treat a portion of fluoroplastic substrate. When using anonporous fluoroplastic substrate, either a first major surface of thefluoroplastic substrate may be contacted with the composition (yieldinga single-sided hydrophilic fluoroplastic substrate) or both the firstmajor surface and the opposing second major surface may be contactedwith the composition (yielding a dual-sided hydrophilic fluoroplasticsubstrate).

The composition remains in contact with the fluoroplastic substrate fora time sufficient for the radical sites to initiate polymerization withthe grafting monomers and complete the grafting process. As a result,the surface-treated fluoroplastic substrate comprises grafted monomers,oligomers (typically no more than 100 monomer units), and polymers(greater than 100 monomer units) attached to the surfaces thereof.

In the method of the present disclosure, it is desirable to remove thepresence of oxygen so as not to hinder the free radical polymerizationof the grafting monomers (e.g., 4-acryloylmorpholine and optional secondmonomer). This can be accomplished by controlling the environment duringthe process to minimize the amount of oxygen present.

In one embodiment of the present disclosure, the fluoroplastic substrateand the composition are sandwiched (i.e., positioned) between aremovable carrier layer and a removable cover layer to form multilayersandwich structure. Removable cover layer and removable carrier layermay comprise any inert sheet material that is capable of providingtemporary protection to the fluoroplastic substrate and composition fromdirect exposure to oxygen. Suitable inert sheet materials for formingremovable cover layer and removable carrier layer include, but are notlimited to, polyethylene terephthalate film material, other aromaticpolymer film materials, and any other polymer film material thatexhibits a reduced ability to generate free radicals upon irradiationwith the ionizing radiation. Once assembled, the multilayer sandwichstructure comprising the fluoroplastic substrate and the compositioncomprising the 4-acryloylmorpholine proceed to the irradiation step.After exposure to radiation, the removable carrier layer and theremovable cover layer are allowed, but not required, to remain on thesurface-treated fluoroplastic substrate for a period of time prior toremoval so as to provide prolonged protection of surface-treatedfluoroplastic substrate from exposure to oxygen. Desirably, removablecarrier layer and removable cover layer remain on surface-treatedfluoroplastic substrate for at least 15, 30, or even 60 seconds afterbeing irradiated. In one embodiment, the removable carrier layer and/orremovable cover layer can remain intact with the surface-treatedfluoroplastic substrate for an extended time period as would be the caseif batch processing rolls of multilayer sandwich structure are prepared.Exclusion of oxygen in a multilayer sandwich allows free radicalchemistry to continue after radiation exposure for a duration sufficientto improve the grafting yield. The removable carrier layer and/orremovable cover layer can be removed and the surface-treatedfluoroplastic substrate can proceed to optional steps, includingwashing/rinsing, drying, and/or heating or further treatment of thegrafted surface of the fluoroplastic substrate. This method worksparticularly well in batch processing where the composition is contactedwith the fluoroplastic substrate prior to irradiation.

In another embodiment of the present disclosure, the fluoroplasticsubstrate is exposed to the radiation in an inert atmosphere. Generally,the fluoroplastic substrate is placed in a chamber purged of oxygen.Typically, the chamber comprises an inert atmosphere such as nitrogen,carbon dioxide, helium, argon, etc. with a minimal amount of oxygen,which is known to inhibit free radical polymerization. Followingirradiation, the fluoroplastic substrate is transported in an inertenvironment and contacted with the composition, where it is again storedin an inert environment and allowed to react.

The irradiation step involves the irradiation of substrate surfaces withionizing radiation to prepare free radical reaction sites on suchsurfaces upon which the monomers are subsequently grafted. “Ionizingradiation” means e-beam, gamma, and x-ray radiation of a sufficient doseand energy to cause the formation of free radical reaction sites on thesurface(s) of the fluoroplastic substrate. The radiation is ofsufficiently high energy that when absorbed by the fluoroplasticsubstrate, chemical bonds in the substrate are cleaved and free radicalsites generated. Free radical sites on the surface of the substrate canreact with the carbon-carbon double bond of 4-acryloylmorpholine (oroptional second monomer), which can continue to add 4-acryloylmorpholine(or optional second monomer) via a free radical, addition (or chain)polymerization. Other reactions are also possible. For example, when thecomposition and substrate are in contact during the irradiation step,free radicals can be generated in both the composition and substrate.Free radicals in the composition can initiate polymerization of4-acryloylmorpholine, and optionally other polymerizable monomerspresent, and the resultant monomeric, oligomeric, and polymeric activefree radical species can couple with free radical sites on thesubstrate.

In the present disclosure, the ionizing radiation is selected frome-beam, x-ray, and/or gamma radiation. These radiation sources are ableto penetrate through solids, such that the fluoropolymer substrate wouldnot act as a mask during the irradiation. This is particularlyadvantageous when surface-treating a porous fluoroplastic substratecomprising a complicated network of pores. The radiation source may beselected depending on the application. For example, E-beam usesaccelerated electrons while gamma irradiation usesradioisotope-generated gamma rays in a continuous exposure mode. Thusgamma is more penetrating in irradiation than e-beam and is more suitedfor irradiating denser materials. As e-beam is powered by electricity,it can provide significantly higher irradiation dose rate and thereforerequire significantly less time. E-beam is perhaps better suited forcontinuous or semi-continuous web-based process while gamma can treatdense and bulky materials. X-ray is similar to gamma although theradiation is generated in a different manner. Gamma involves radioactivedecay while x-rays are Bremstrahlung radiation generated fromaccelerating electrons into a metal target. X-ray tubes generally emitslightly longer wavelengths and lower photon energies than a gammasource. Depending on product density, product packaging, and/or desiredprocessing mode, one irradiation method may be selected over the other.For example, e-beam irradiation provides significantly higher dose ratesand therefore requires significantly less irradiation time than gammairradiation. Thus, e-beam irradiation is more suited for continuous orsemi-continuous web-based processes than gamma irradiation. Gammairradiation may be more suited for batch processes and the surfacetreatment of large objects or a collection of objects that isvoluminous.

In the irradiation step, the fluoroplastic substrate (or fluoroplasticsubstrate comprising the composition) is exposed to ionizing radiationinside a chamber. The chamber may contain at least one source capable ofproviding a sufficient dose of radiation. A single source is typicallycapable of providing a sufficient dose of radiation, although two ormore sources and/or multiple passes through a single source may be used.

Dose is the total amount of energy absorbed per mass unit. Dose iscommonly expressed in kilograys (kGy). A Gray is defined as the amountof radiation required to supply 1 joule of energy per kilogram of mass.

Generally, the fluoroplastic substrate is purged (e.g. for two minutesor more) of oxygen using nitrogen or another inert gas because oxygeninhibits free-radical polymerization. The chamber is also often purgedof oxygen using an inert gas. This purging can facilitate polymerizationand high conversion in a desired period of time. A higher dose rate or alonger exposure time would be needed to achieve a similar degree ofpolymerization absent purging if a significant amount of oxygen werepresent. Both of which could impair or diminish the bulk mechanicalproperties of the fluoroplastic substrate. Exposing the irradiatedsubstrate to the standard atmosphere quenches all free radicals at thesurface of the substrate and prohibits grafting of the monomer(s).However, purging is not necessary when the substrate is isolated toexclude addition of oxygen during irradiation. For example, thefluoroplastic substrate may be sandwiched between oxygen barrier films.While exclusion of all oxygen is desirable, in practice, a minimalamount of oxygen is present.

In one embodiment, the fluoroplastic substrate comprising thecomposition is positioned in proximity to an irradiation source.Preferably the fluoroplastic substrate is irradiated in a substantiallyuniform manner by proper positioning of the source(s) in relation to thesubstrate, or agitating several substrates or objects duringirradiation.

Electron beams (e-beams) are generally produced by applying high voltageto tungsten wire filaments retained between a repeller plate and anextractor grid within a vacuum chamber maintained at about 10⁻⁶ Torr.The filaments are heated at high current to produce electrons. Theelectrons are guided and accelerated by the repeller plate and extractorgrid towards a thin window of metal foil. The accelerated electrons,traveling at speeds in excess of 10⁷ meters/second (m/sec) andpossessing about 150 to 300 kilo-electron volts (keV), pass out of thevacuum chamber through the foil window and penetrate whatever materialis positioned immediately beyond the foil window.

The quantity of electrons generated is directly related to the extractorgrid voltage. As extractor grid voltage is increased, the quantities ofelectrons drawn from the tungsten wire filaments increase. E-beamprocessing can be extremely precise when under computer control, suchthat an exact dose and dose rate of electrons can be directed toward thefluoroplastic substrate (or fluoroplastic substrate comprising thecomposition).

Electron beam generators are commercially available from a variety ofsources, including the ESI “ELECTROCURE” EB SYSTEM from Energy Sciences,Inc. (Wilmington, Mass.), and the BROADBEAM EB PROCESSOR from PCTEngineered Systems, LLC (Davenport, Iowa). For any given piece ofequipment and irradiation sample location, the dosage delivered can bemeasured in accordance with ASTM E-1275 entitled “Practice for Use of aRadiochromic Film Dosimetry System.” By altering extractor grid voltage,beam current, beam diameter and/or distance to the source, various doserates can be obtained. Typical dose rates may range from 0.03 to 1000kGy/sec.

Dose for the e-beam are dependent upon a number of processingparameters, including voltage, speed, and beam current. Dose can beconveniently regulated by controlling line speed, and the currentsupplied to the extractor grid. A target dose (e.g., 20 kGy) can beconveniently calculated by multiplying an experimentally measuredcoefficient (a machine constant) by the beam current and dividing by theweb speed to determine the exposure. The machine constant varies as afunction of beam voltage.

In one embodiment, using an e-beam radiation source, a controlled amountof dosage ranging from a minimum dosage of about 10 kilograys (kGy) to amaximum dosage of about 100 kGy is delivered. Typically, the totalcontrolled amount of dosage ranges from about 20 kGy to about 60 kGy.

Generally, suitable gamma ray sources emit gamma rays having energies of400 keV or greater. Typically, suitable gamma ray sources emit gammarays having energies in the range of 500 keV to 5 MeV. Examples ofsuitable gamma ray sources include cobalt-60 isotope (which emitsphotons with energies of approximately 1.17 and 1.33 MeV in nearly equalproportions) and cesium-137 isotope (which emits photons with energiesof approximately 0.662 MeV). The distance from the source can be fixedor made variable by changing the position of the target or the source.The flux of gamma rays emitted from the source generally decays with thesquare of the distance from the source and duration of time as governedby the half-life of the isotope. In general, the dose rate is determinedby the source strength at the time of irradiation and the distance fromthe source to the target (e.g. fluoroplastic substrate). Typical doserates may range from 0.000003 to 0.03 kGy/sec.

Once a dose rate has been established, the absorbed dose is accumulatedover a period of time. During this period of time, the dose rate mayvary if the fluoroplastic substrate (or fluoroplastic substratecomprising the composition) is in motion or other absorbing objects passbetween the source and sample. For any given piece of equipment andirradiation sample location, the dosage delivered can be measured inaccordance with ASTM E-1702 entitled “Practice for Dosimetry in a GammaIrradiation Facility for Radiation Processing”. Dosimetry may bedetermined per ASTM E-1275 entitled “Practice for Use of a RadiochromicFilm Dosimetry System” using GEX B3 thin film dosimeters. Typical dosesrange from 1 to 50 kGy.

The total dose of gamma radiation received by the fluoroplasticsubstrate (or fluoroplastic substrate comprising the composition)depends on a number of parameters including source activity, residencetime (i.e. the total time the sample is irradiated), the distance fromthe source, and attenuation by the intervening cross-section ofmaterials between the source and sample. Dose is typically regulated bycontrolling residence time, distance to the source, or both.

The total dose of ionizing radiation (e-beam, x-ray, or gamma) receivedby the fluoroplastic substrate (or fluoroplastic substrate comprisingthe composition) can affect the extent of polymerization. The doseneeded for polymerization depends on a variety of factors including, forexample, the materials used, the concentration of monomers in thecomposition, the presence and amount of chain transfer agent, thepresence and amount of free radical inhibitors or free radicalscavengers present, such as dissolved oxygen, the physical dimensions ofthe substrate and arrangement of substrates, and the desired properties.

Generally, doses in the range of about 1 to 100 kGy and dose rates inthe range of 0.000003 to 1000 kGy/sec are suitable. However, nolimitations are placed on the dose or dose rate. Total dose requirementfor any given composition will vary as a function of the dose rate.Higher dose rates typically result in faster chain termination and moreungrafted polymer formation. Thus, a dose rate can be selected based ondesired properties for a specified composition.

Once the fluoroplastic substrate (or fluoroplastic substrate comprisingthe composition) has been irradiated to a desired dose, the substratebearing grafted polymer groups may be optionally rinsed and/or heated toremove ungrafted materials. In the optional rinsing step, thesurface-treated fluoroplastic substrate is washed or rinsed one or moretimes to remove any unreacted monomers, ungrafted polymer, solvent orother reaction by-products. Typically, the surface-treated fluoroplasticsubstrate is washed or rinsed up to three times using a water rinse, analcohol rinse, a combination of water and alcohol rinses, and/or asolvent rinse (e.g. acetone, methyl ethyl ketone, etc). When an alcoholrinse is used, the rinse may include one or more alcohols including, butnot limited to, isopropanol, methanol, ethanol, or any other alcoholthat is practical to use and an effective solvent for any residualmonomer. In each rinse step, the surface-treated fluoroplastic substratemay pass through a rinse bath or a rinse spray.

In one embodiment, the method further comprises an optional drying step,the surface-treated fluoroplastic substrate is dried to remove any rinsesolution. Typically, the surface-treated substrate is dried in ovenhaving a relatively low oven temperature for a desired period of time.Oven temperatures typically range from about 60° C. to about 120° C.,while oven dwell times typically range from about 120 to about 600seconds. Any conventional oven may be used in the optional drying step.It should also be noted that in other embodiments the drying step canproceed before the rinsing step to eliminate volatile components beforeextraction of non-grafted residue. Following the optional drying step,the dried surface-treated fluoroplastic substrate can be taken up inroll form to be stored for future use.

In one embodiment, additional process steps may be used, including, butare not limited to, a reaction step or a coating step wherein a coatingcomposition is applied to the surface-treated fluoroplastic substrate.For example, a lamination step wherein one or more additional layers aretemporarily or permanently joined to the surface-treated fluoroplasticsubstrate, an assembling step wherein the surface-treated fluoroplasticsubstrate is combined with one or more additional components to form afinished product (e.g., a filter assembly), a packaging step thesurface-treated fluoroplastic substrate or a finished product comprisingthe surface-treated fluoroplastic substrate is packaged within a desiredpackaging material (e.g., a polyethylene film or bag), or anycombination thereof.

By following the methods disclosed herein, monomers and/orinterpolymerized monomer units (i.e., monomers that are polymerizedtogether to form a polymer backbone) of 4-acryloylmorpholine, whichoptionally may include second monomers, are grafted onto the surface ofthe fluoroplastic substrate, altering the properties of thesurface-treated fluoroplastic substrate, e.g., making it hydrophilic.

The present disclosure reduces or eliminates many of the known problemsassociated with fluoroplastic substrates including, but not limited to,for example wetting issues, and reduced flux. Because the surfacetreatment is covalently bonded to the fluoroplastic substrate, it ismore durable than surface treatments that may just be in physicalcontact. In addition, the amide linkage of the 4-acryloylmorpholine ismore resistant to hydrolysis than ester linkages present in surfacetreatments comprising (meth)acrylates. The present disclosure alsoenables the formation of surface-treated substrates having variousdegrees of hydrophilicity depending on the materials and steps used toform a given surface-treated fluoroplastic substrate.

The grafting of monomers including 4-acryloylmorpholine to the surfaceof the fluoroplastic substrate enhances the hydrophilicity of anotherwise hydrophobic substrate.

In one embodiment, the resulting surface-treated fluoroplastic substratehas a critical surface tension of at least 45, 50, 55, 60, 65, or even70 dyne/cm.

In one embodiment, the resulting surface-treated, porous fluoroplasticsubstrate has a “critical wetting surface tension” (CWST) of at least 10dynes/cm, at least 15 dynes/cm or even at least 20 dynes/cm, greaterthan the non-surface treated fluoroplastic substrate. By “criticalwetting surface tension” (CWST) is meant the surface tension of a liquidthat would just penetrate or be absorbed into a porous substrate, withany slight increase in the surface tension of the liquid causing it tonot penetrate or be absorbed into the substrate. The CWST of a poroussubstrate may be measured using the Critical Wetting Surface Tension(CWST)—Penetrating Drop method described herein, whereby a series oftest solutions of increasing surface tension is applied to the samplesuntil a solution of such high surface tension is used that it no longerpenetrates the substrate. The surface tension of the previously usedsolution is then recorded as the CWST of the substrate.

In one embodiment of the present disclosure, the surface-treatedfluoroplastic substrate is porous and has a water flux (flowrate dividedby lateral area) that is greater than zero, and the water flux of thesurface-treated fluoroplastic substrate is maintained or greater thanthe initial water flux of the untreated porous fluoroplastic substrate.

One method of measuring the water flux of a given surface-treatedfluoroplastic substrate or porous untreated fluoroplastic substrate isto measure the amount of time necessary for a quantity of water to flowthrough a surface-treated porous fluoroplastic substrate or untreatedporous fluoroplastic substrate of the same lateral dimensions or area ata constant temperature and pressure. A decrease in the amount of timenecessary for a quantity of water at a constant temperature and pressureto flow through a given surface-treated fluoroplastic substrate comparedto the corresponding fluoroplastic substrate prior to surfacemodification indicates an increase in the water flux of thesurface-treated fluoroplastic substrate. Advantageously, in oneembodiment the method of the present disclosure improves not only thehydrophilicity of the fluoroplastic substrate, but also maintains orimproves the flux.

In one embodiment, the resulting surface-treated fluoroplastic substratehas a water static contact angle of at least 15 degrees, 25 degrees, 30degrees, 40 degrees, 50 degrees, or even 60 degrees less than theuntreated fluoroplastic substrate.

In one embodiment, when the surface-treated fluoroplastic substrates ofthe present disclosure are porous, they may be particularly suited asfilter media. For examples, the surface-treated fluoroplastic substratesof the present disclosure may be used in the filtering of liquid,specifically aqueous solutions. As the polymer is grafted to render ithydrophilic, the hydrophilicity is durable.

In one embodiment of the present disclosure, the surface-treatedfluoroplastic substrates of the present disclosure may be used inmicrofiltration (i.e., retaining particles with particle sizes in therange of 0.1 to 10 micrometers) or ultrafiltration (i.e., retainingparticles with particle sizes in the range of 2 to 100 nanometers)applications.

Exemplary embodiments of the present invention are described below:

Embodiment 1

A method of treating a fluoroplastic substrate comprising:

-   -   (a) providing a fluoroplastic substrate comprising a polymer        having a structural unit selected from —CHF—, —CH₂CF₂—, or        —CF₂CH₂—;    -   (b) contacting the fluoroplastic substrate with a composition        comprising 4-acryloylmorpholine; and    -   (c) exposing the fluoroplastic substrate to a controlled amount        of ionizing radiation selected from at least one of: e-beam,        x-ray, and gamma radiation so as to form a surface treatment on        the fluoroplastic substrate comprising a grafted,        radiation-initiated reaction product of the composition attached        to the surfaces of the fluoroplastic substrate.

Embodiment 2

The method of embodiment 1, wherein the fluoroplastic substrate is firstcontacted with the composition and then exposed to the controlled amountof radiation.

Embodiment 3

The method of embodiment 1, wherein the fluoroplastic substrate is firstexposed to the controlled amount of radiation and then contacted withthe composition.

Embodiment 4

The method of any one of the previous embodiments, wherein thecomposition further comprises diacetone acrylamide.

Embodiment 5

The method of any one of the previous embodiments, wherein thefluoroplastic substrate comprises a series of interconnected pores froma first major surface to an opposing second major surface.

Embodiment 6

The method of embodiment 5, wherein the fluoroplastic substrate is aporous membrane with a symmetric, asymmetrically, or a multizone porousstructure.

Embodiment 7

The method of any one of the previous embodiments, wherein thefluoroplastic substrate is selected from a thermally-induced phaseseparation (TIPS) membrane, a solvent-induced phase separation (SIPS)membrane, or a combination thereof.

Embodiment 8

The method of any one of embodiments 1-7, wherein the fluoroplasticsubstrate is a non-woven.

Embodiment 9

The method of any one of the previous embodiments, wherein thefluoroplastic substrate is selected from at least one of a homopolymerof vinyl fluoride; a homopolymer of vinylidene fluoride; a copolymercomprising vinylidene fluoride; a copolymer of ethylene andchlorotrifluoroethylene; a copolymer of ethylene andtetrafluoroethylene; a copolymer of vinylidene fluoride andchlorotrifluoroethylene; and a copolymer of vinylidene fluoride,hexafluoropropylene, and tetrafluoroethylene.

Embodiment 10

The method of any one of the previous embodiments, wherein thecomposition further comprises methanol.

Embodiment 11

A surface-treated fluoroplastic substrate made from the method of anyone of the previous embodiments.

Embodiment 12

An article comprising:

a porous fluoroplastic substrate comprising a polymer having structuralunit selected from —CHF—, —CH₂CF₂—, or —CF₂CH₂— and having interstitialand outer surfaces; and

a surface-treatment thereon the porous fluoroplastic substrate, whereinthe surface-treatment is a grafted reaction product of a compositioncomprising 4-acryloylmorpholine.

Embodiment 13

The article of embodiment 12, wherein the pores are 5 nm to 30micrometers in size.

Embodiment 14

The article of any one of embodiments 12-13, wherein the porousfluoroplastic substrate is a symmetric, asymmetrically, or a multizoneporous structure.

Embodiment 15

The article of any one of embodiments 12-14, further comprising anadditional layer, wherein the additional layer is porous and is indirect contact with the article.

Embodiment 16

The article of embodiment 15, wherein the additional layer is anon-woven.

Embodiment 17

The article of any one of embodiments 15-16, wherein the pores of theadditional layer are larger than the pores of the fluoroplasticsubstrate.

Embodiment 18

The article of any one of embodiments 12-17, wherein the compositionfurther comprises a second monomer.

Embodiment 19

The article of embodiment 18, wherein the second monomer is diacetoneacrylamide.

Embodiment 20

The article of any one of embodiments 12-19, wherein the fluoroplasticsubstrate is not poly(vinylidene fluoride).

Embodiment 21

The article of any one of embodiments 12-19, wherein the porousfluoroplastic substrate is a non-woven.

Embodiment 22

The article of any one of embodiments 12-19, wherein the porousfluoroplastic substrate is selected from a thermally-induced phaseseparation (TIPS) membrane, a solvent-induced phase separation (SIPS)membrane, or a combination thereof.

Embodiment 23

An article comprising:

a fluoroplastic substrate comprising a polymer having a structural unitselected from —CHF—, —CH₂CF₂—, or —CF₂CH₂— and wherein the fluoroplasticsubstrate is not poly(vinylidene fluoride); and

a surface-treatment thereon the fluoroplastic substrate, wherein thesurface-treatment is a grafted reaction product of a compositioncomprising 4-acryloylmorpholine.

Embodiment 24

The article of embodiment 23, wherein the composition further comprisesa second monomer.

Embodiment 25

The article of embodiment 24, wherein the second monomer is diacetoneacrylamide.

Embodiment 26

The article of any one of embodiments 23-25, further comprising anadditional layer, wherein the additional layer is in direct contact withthe article.

Embodiment 27

The article of embodiment 26, wherein the surface-treated side of thefluoroplastic substrate is in direct contact with the additional layer.

Embodiment 28

The article of embodiment 26, wherein the surface-treated side of thefluoroplastic substrate is not in direct contact with the additionallayer.

Embodiment 29

An article comprising:

a fluoroplastic substrate comprising a polymer having a structural unitselected from —CHF—, —CH₂CF₂—, or —CF₂CH₂—; and

a surface-treatment thereon the fluoroplastic substrate, wherein thesurface-treatment is a grafted reaction product of a compositioncomprising 4-acryloylmorpholine and a second monomer.

Embodiment 30

The article of embodiment 29, wherein the second monomer is diacetoneacrylamide.

Embodiment 31

The article of any one of embodiments 29-30, wherein the fluoroplasticsubstrate is a porous fluoroplastic substrate.

Embodiment 32

The article of embodiment 31, wherein the pores are 5 nm to 30micrometers in size.

Embodiment 33

The article of any one of embodiments 31-32, wherein the fluoroplasticsubstrate is a symmetric, asymmetrically, or a multizone porousstructure.

Embodiment 34

The article of any one of embodiments 29-33, further comprising anadditional layer, wherein the additional layer is in direct contact withthe article.

Embodiment 35

The article of embodiment 34, wherein the additional layer is a poroussubstrate.

Embodiment 36

The article of 35, wherein the porous substrate is a non-woven.

Embodiment 37

A method of filtering a liquid comprising:

contacting a liquid to the surface-treated fluoroplastic substrateaccording to embodiment 11.

Embodiment 38

The method of embodiment 37, wherein the liquid comprises water.

Embodiment 39

A method of filtering a liquid comprising:

contacting a liquid to the article according to any one of embodiments23-36.

Embodiment 40

A graft copolymer composition comprising a fluoropolymer that is graftedto at least one of: a monomer, an oligomer, and a polymer formed from amonomer comprising 4-acryloylmorpholine; wherein the fluoropolymer isformed from monomers comprising (i) ethylene andchlorotrifluoroethylene, (ii) ethylene and tetrafluoroethylene, (iii)vinylidene fluoride and chlorotrifluoroethylene, or (iv)tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride.

The present invention is described above and further illustrated belowby way of examples, which are not to be construed in any way as imposinglimitations upon the scope of the invention. On the contrary, it is tobe clearly understood that resort may be had to various otherembodiments, modifications, and equivalents thereof which, after readingthe description herein, may suggest themselves to those skilled in theart without departing from the spirit of the present invention and/orthe scope of the appended claims.

EXAMPLES

Advantages and embodiments of this disclosure are further illustrated bythe following examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. In theseexamples, all percentages, proportions and ratios are by weight unlessotherwise indicated.

All materials are commercially available, for example from Sigma-AldrichChemical Company; Milwaukee, Wis., or known to those skilled in the artunless otherwise stated or apparent. Materials (monomers and solvents)were used as received unless indicated otherwise.

These abbreviations are used in the following examples: g=gram,kg=kilograms, min=minutes, mol=mole; cm=centimeter, mm=millimeter,ml=milliliter, L=liter, psi=pressure per square inch, MPa=megaPascals,s=second; vol=volume; and wt=weight.

Test Methods

Critical Wetting Surface Tension (CWST)—Penetrating Drop Method

The critical wetting surface tension of the samples was determined byuse of the penetrating drop method outlined in Journal of MembraneScience, 33, 315-328 (1987) “Wetting Criteria for the Applicability ofMembrane Distillation” as follows. A series of test solutions ofincreasing surface tension up to 72 dyne/cm (available under the tradedesignation “DYNE TEST SOLUTIONS” available from Jemmco LLC., Mequon,Wis.) were applied at increasing surface tensions to the samples. As theCWST was approached, test solutions at 1 dyne/cm interval were useduntil a test solution no longer penetrated or absorbed into themembrane, but beaded up on the sample surface and remained beaded up forat least about 2 seconds. The surface tension of the test solutiontested just prior to this beaded up test solution was then recorded asthe CWST. If the test solution of highest surface tension, 72 dyne/cm,penetrated the sample and did not bead up, then the CWST was recordedas >72 dyne/cm, i.e., greater than 72 dyne/cm.

Inverse Flow Rate

The amount of time it took for 100 ml deionized water to pass throughthe membrane was conducted as follows. A circular disk of the membranehaving a diameter of approximately 47 mm was punched out from the 14cm×16 cm membrane sample, and placed in a Model 4238 Pall Gelmanmagnetic filter holder (available from Pall Corp., East Hills, N.Y.).The filter holder was then placed on a filter flask that was attached toa vacuum pump. A vacuum gauge was used to monitor the vacuum. 250 ml ofdeionized water were placed in the filter holder over the membrane andthen a vacuum of 23 inches of mercury (584 mm Hg) was applied. After thefirst 50 ml of water had passed through the membrane, the time wasrecorded for the next 100 ml of water to pass through the membrane andreported as Time.

Bubble Point Pore Size

The bubble point pore size can be measured using a forward flow bubblepoint pressure apparatus as follows. A disc of the membrane is saturatedwith a mixture of 60 vol % isopropyl alcohol and 40 vol % water andmount in a 90 mm diameter membrane holder. A pressure controller (Type640, available from MKS Instruments, Inc.) can be used to regulate thesupply of nitrogen gas to the upstream side of the membrane. The massflow of gas downstream of the membrane is measured using a mass flowmeter (available under the trade designation “MASS-FLO” meter, model no.179A12CS3BM, from MKS Instruments, Inc.). At the beginning of the test,nitrogen gas is supplied to the upstream side of the membrane at apressure of 10.3 kPa (1.5 psi). The pressure is then raised byincrements of 1.38 kPa (0.2 psi) every 0.2 second. This results in ameasured mass flow downstream of the membrane that is initially roughlyconstant at a value representative of the rate of diffusional flow ofnitrogen through the liquid-filled pores of the membrane, followed by amonotonic increase in the measured mass flow as liquid is displaced fromthe pores. The bubble point pressure of the membrane is taken as theapplied nitrogen pressure at the onset of the monotonic increase inmeasured mass flow. The bubble point pressure of a membrane is inverselyrelated to the largest pore size in the pore size distribution, or thebubble point pore size, according to the LaPlace equation.

Porosity

The porosity of the membrane was determined by weighing a sample ofmeasured lateral area and thickness. The weight of the identical volume(from the lateral area and thickness of the membrane) of pure polymerwas calculated from the density of the pure polymer. The porosity wascalculated by the following equation:

Porosity (%)=100−100×[wt. of membrane with volume Y/wt. of polymer withvolume Y]

Hansen Solubility Parameters

Hansen solubility parameters were calculated using the parameterizedmethod of Hansen described in “Hansen Solubility Parameters: A User'sHandbook” by Charles M. Hansen, copyright 2000, CRC Press LLC (NewYork).

Materials

-   -   AMP—4-Acryloylmorpholine, Sigma-Aldrich, Milwaukee Wis.    -   Betaine—N,N-dimethyl-N-(3-sulfopropyl)-3′-methacryloylaminopropanaminium        inner salt, Sigma-Aldrich    -   DAA—Diacetone Acrylamide, Sigma Aldrich    -   ECTFE—a copolymer of ethylene and chlorotrifluoroethylene        (available under the trade designation “HALAR 902 ECTFE” from        Solvay Specialty Polymers; Thorofare N.J.)    -   ETFE—a copolymer of ethylene and tetrafluoroethylene (available        under the trade designation “3M DYNEON FLUOROPLASTIC ET 6235”        from 3M Co., St. Paul Minn.)    -   FEP—a copolymer of tetrafluoroethylene and hexafluoropropylene,        which can be available under the trade designation “3M DYNEON        FEP” from 3M Company    -   HEA—N-(2-Hydroxyethyl)acrylamide, Sigma Aldrich    -   Methanol—methanol OmniSolv High Purity Solvent available from        EMD Chemicals, Inc., Gibbstown N.J.    -   MPA—N-(3-Methoxypropyl)acrylamide, Sigma-Aldrich    -   NVP—N-Vinylpyrrolidone, Sigma Aldrich    -   PVDF—a homopolymer of vinylidene fluoride, high molecular weight        grade, available under the trade designation “DYNEON PVDF        1012/0001” from 3M Company    -   THV 500—a polymer of tetrafluoroethylene, hexafluoropropylene,        and vinylidene fluoride (available under the trade designation        “3M DYNEON FLUOROPLASTIC 500” from 3M Company, St. Paul Minn.)    -   THV 610—a polymer of tetrafluoroethylene, hexafluoropropylene,        and vinylidene fluoride (available under the trade designation        “3M DYNEON FLUOROPLASTIC 610” from 3M Company, St. Paul Minn.)

Preparation of Substrates

Porous Membrane I was prepared with a TIPS process using ECTFE accordingto U.S. Patent Publication No. 2011/0244013 (Mrozinski et al.). Themembrane had a thickness of approximately 50 microns (2 mils), a BubblePoint Pore Size of 280 nanometers and a Porosity of 64%.

Porous Membrane II was prepared with a TIPS process using PVDF accordingto U.S. Pat. No. 7,338,692 (Smith et al.). The membrane had a thicknessof approximately 115 microns (4.6 mils), a Bubble Point Pore Size of1200 nanometers and a Porosity of 67%.

Nonporous film III was prepared with ECTFE by melt pressing the pelletsat approximately 250° C. to form a film having a thickness ofapproximately 250 microns (10 mils).

Nonporous films IV, V, VI and VII were prepared by extruding resinpellets THV 500, THV 610, ETFE, and FEP, respectively, according to themanufacturer's recommendations for processing. The films were thefollowing approximate thicknesses: THV 500 was 100 μm (4 mils); THV 610was 25 μm (1 mil); ETFE was 250 μm (10 mils); and FEP was 25 μm (1 mil).

Preparation of Treated Substrates

Porous membrane (approximately 14 cm×16 cm) or nonporous film(approximately 10 cm×12 cm) were placed between two slightly largersheets of 100 micron (4 mil) thick polyethylene terephthalate (PET)film, and the PET films taped together on one side. This sandwich wasthen opened and the substrate was wetted with a 25 wt. % monomer(s) inmethanol solution, and the sandwich reclosed. Trapped air bubbles wereremoved and excess liquid squeezed out by applying a plastic roller overthe surface of the sandwich. The web pathway through the electron beamprocessor was under a constant nitrogen purge such that the oxygen levelwas 30 to 50 ppm, or less. Approximately 5-10 min after the substratewas contacted with the solution, the sandwich was conveyed through anelectron beam processor (ESI CB-300 Electrocurtain electron beam system,Energy Systems, Inc., Wilmington, Mass.) at a speed of about 21 feet perminute and at a voltage of 240 KeV with sufficient beam current appliedto the cathode to deliver a dose of 4 Mrad (40 kGy). The web pathwaythrough the electron beam processor was still under the nitrogen purge.The beam was calibrated using thin film dosimeters. After about morethan 30 minutes following irradiation with the e-beam, the treatedsubstrates were removed from between the PET and washed by placing infour sequential baths of deionized water, deionized water, deionizedwater, and lastly methanol for approximately 4-6 minutes per bath. Thetreated substrates were allowed to air dry for at least 5 days and thenthe samples were tested for “Critical Wetting Surface Tension” and“Inverse Flow Rate” following the test methods described above.

Example 1 and Comparative Examples C1-C6

Treated membranes (Example 1 and Comparative Examples C2-C6) wereprepared by according to the “Preparation of Treated Substrates”procedure described above using Porous Membrane I and 25 wt % solutionsof the monomers shown in Table 1. The resulting membranes and anuntreated membrane of Porous Membrane I (Comparative Example C1) weretested for CWST and Inverse Flow Rate. The results are shown in Table 1.

TABLE 1 Hansen Solubility CWST Time Example Monomer parameter(MPa^(0.5)) (dyne/cm) (s) 1 AMP 23.4 62 81 C1 None 37 123 C2 NVP 26.6 4585 C3 MPA 20.9 44 77 C4 Betaine NC 40 87 C5 DAA 20.9 52 100 C6 HEA 28.553 132 NC = not calculated—a zwitterionic compound

Examples 2-8, Comparative Examples C7-C8

Treated membranes were prepared by the “Preparation of TreatedSubstrates” process described above using Porous Membrane I and 25 wt %solutions of the monomer or monomer mixtures shown in Table 2. Theresulting membranes were tested for CWST and Inverse Flow Rate. Theresults are shown in Table 2.

TABLE 2 Monomers (wt. % based on CWST Time Example total wt. ofmonomers) (dyne/cm) (s) 2 100 AMP 69 94 3 60/40 AMP/NVP 61 88 4 40/60AMP/NVP 60 80 C7 100 NVP 42 93 5 80/20 AMP/HEA 57 122 6 60/40 AMP/HEA 5593 7 40/60 AMP/HEA 53 97 8 20/80 AMP/HEA 58 101 C8 100 HEA 59 212

Examples 9-18 and Comparative Example C9

Treated membranes were prepared by the “Preparation of TreatedSubstrates” process described above using Porous Membrane I and 25 wt %solutions of the monomer or monomer mixtures shown in Table 3. Theresulting membranes were tested for CWST and Inverse Flow Rate. Theresults are shown in Table 3.

TABLE 3 Monomers (Wt. CWST Example AMP/Wt. DAA) (dyne/cm) Time (s)  9100/0 69 123 10  90/10 71 110 11  80/20 71 115 12  70/30 71 140 13 60/40 71 102 14  50/50 65 96 15  40/60 70 103 16  30/70 67 114 17 20/80 57 109 18  10/90 58 112 C9  0/100 56 115

Examples 19-20 and Comparative Example C10

Treated membranes were prepared by the “Preparation of TreatedSubstrates” process described above using Porous Membrane II and 25 wt %solutions of the monomer shown in Table 4. The treated membranes and anuntreated membrane of Porous Membrane II (Comparative Example C10) weretested for CWST and Inverse Flow Rate. The results are shown in Table 4.

TABLE 4 Example MONOMER CWST (dyne/cm) Time (s) C10 NONE 47 33 19AMP >72 25 20 AMP >72 27

Examples 21-24 and Comparative Examples C11-C16

Nonporous Films III-VII were washed in isopropanol and allowed to airdry before treatment. Treated substrates (Examples 21-24 and ComparativeExample 16) were prepared according to the “Preparation of TreatedSubstrates” procedure described above using Nonporous Films III-VII anda 25 wt. % solution of 4-acryloylmorpholine monomer. During treatment,the construction was passed through the e-beam with the surface of thenonporous film initially wetted with and contacting the4-acryloylmorpholine monomer solution facing the e-beam source.Comparative examples C11-C15, were the untreated Nonporous FilmsIII-VII, which were also washed in isopropanol and allowed to air drybefore testing. Examples 21-24 and Comparative Examples C11-C16 werethen tested for water static contact angles as follows. Four drops ofdeionized water each of approximately 2 microliters in volume wereplaced on the top surface of each film, the treated surface of thetreated substrates, and the contact angles were measured using agoniometer. The results for each of the 4 sessile drops were averagedand are shown in Table 5.

TABLE 5 Example Nonporous film Contact angle, degrees C11 III 102.6 21III 38.9 C12 IV 97.9 22 IV 26.0 C13 V 103.7 13 V 46.9 C14 VI 96.8 24 VI64.4 C15 VII 110.5 C16 VII 102.9

Foreseeable modifications and alterations of this invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. This invention should not be restricted tothe embodiments that are set forth in this application for illustrativepurposes. To the extent that there is a conflict or discrepancy betweenthis specification and the disclosure in any document incorporated byreference herein, this specification will control.

What is claimed is:
 1. An article comprising: a porous fluoroplasticsubstrate comprising at least one of a copolymer of ethylene andchlorotrifluoroethylene or a copolymer of ethylene andtetrafluoroethylene and having interstitial and outer surfaces; and asurface-treatment thereon the porous fluoroplastic substrate, whereinthe surface-treatment is a grafted reaction product of a compositioncomprising 4-acryloylmorpholine.
 2. The article of claim 1, wherein thepores are 5 nm to 30 micrometers in size.
 3. The article of claim 1,further comprising an additional layer, wherein the additional layer isporous and is in direct contact with the article.
 4. The article ofclaim 3, wherein the pores of the additional layer are larger than thepores of the fluoroplastic substrate.
 5. The article of claim 1, whereinthe porous fluoroplastic substrate is not poly(vinylidene fluoride). 6.The article of claim 1, wherein the surface-treatment is a graftedreaction product of a composition comprising 4-acryloylmorpholine and asecond monomer.
 7. The article of claim 6, wherein the second monomer isdiacetone acrylamide.
 8. The article of claim 1, wherein the porousfluoroplastic substrate is a symmetric, asymmetrically, or a multizoneporous structure.
 9. The article of claim 1, wherein the porousfluoroplastic substrate is selected from a thermally-induced phaseseparation (TIPS) membrane, a solvent-induced phase separation (SIPS)membrane, or a combination thereof.
 10. An article comprising: afluoroplastic substrate comprising a polymer having a structural unitselected from —CHF—, —CH₂CF₂—, or —CF₂CH₂— and wherein the fluoroplasticsubstrate is not poly(vinylidene fluoride); and a surface-treatmentthereon the fluoroplastic substrate, wherein the surface-treatment is agrafted reaction product of a composition comprising4-acryloylmorpholine.
 11. The article of claim 10, wherein thecomposition further comprises a second monomer.
 12. The article of claim11, wherein the second monomer is diacetone acrylamide.
 13. The articleof claim 10, further comprising an additional layer, wherein theadditional layer is in direct contact with the article.
 14. An articlecomprising: a fluoroplastic substrate comprising a polymer having astructural unit selected from —CHF—, —CH₂CF₂—, or —CF₂CH₂—; and asurface-treatment thereon the fluoroplastic substrate, wherein thesurface-treatment is a grafted reaction product of a compositioncomprising 4-acryloylmorpholine and a second monomer.
 15. The article ofclaim 14, wherein the second monomer is diacetone acrylamide.
 16. Thearticle of claim 14, wherein the fluoroplastic substrate is a porousfluoroplastic substrate.
 17. The article of claim 14, further comprisingan additional layer, wherein the additional layer is in direct contactwith the article.
 18. The article of claim 14, wherein the fluoropolymeris formed from monomers comprising (i) ethylene andchlorotrifluoroethylene, (ii) ethylene and tetrafluoroethylene, (iii)vinylidene fluoride and chlorotrifluoroethylene, or (iv)tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride.